1. Field of the Invention
The invention relates to injection molding, and particularly to heated bushings which are mounted on the mold providing the possibility of multi-gate locations without the use of runners.
2. Description of the Prior Art
It is known to have a bushing with a central passage and an external heater disposed between the bushing and the mold. However, this is a bulky and cumbersome construction and the excessive heat transfer to the mold could cause distortion of the product. Moreover, the time needed for the steel mold to cool down between cycles lengthened the cycle time.
Yago U.S. Pat. No. 3,797,984 shows a cold sprue injection molding device with an integral sprue chamber and injection nozzle. While this patent is pertinent in that is shows several isolated features of the invention, the Yago system is part of the machine and not an integral part of the mold. Thus, only a single injection point can be accomplished at the price of an expensive apparatus.
Other pertinent patents found in a search are Hendry U.S. Pat. No. 2,746,089, Kelley U.S. Pat. No. 2,911,680 and Putkowski U.S. Pat. No. 3,677,682. While these patents also show isolated elements of the present invention, such as a central passage or an insulating air gap, they fail to teach the entire combination recited in the present claims, nor do they have the advantages of this invention.